Myths about protein skimmer size

[Luca_Brasi]

I have been in the hobby a long time, set up more than 10 reef tanks of various sizes. I also received some formal training and am currently working with the local school system to teach marine bio by maintaining a reef tank in the school. I have come to realize something that I have never seen discussed regarding sump protein skimmers. Specifically that size of tank does not determine size of protein skimmer needed. All protein skimmers say, "for up to a *** gallon tank." I have also seen people talk about going +1 on their skimmers to get extra clean water.

All of these approaches make several huge assumptions. First is that big tanks = big sumps with high flow rate. Sump size and flow rate are perhaps the most important indicators of optimal skimmer size. For example, if you have a 90 gallon tank and go to a 120 gallon tank, keep the same size sump and return pump flow, but add a larger skimmer, all you get is the same amount of suspended material in a bigger skimmer cup.

Here's another way of putting it. The skimmer in the sump only has access to the suspended organic waste material in the sump. It doesn't have access to the waste material in the display tank. Since it can only remove the waste it has access to, you need to increase the sump size and/ or return pump flow to get more production from your skimmer.

I have a 180 gallon reef tank in the school I work for. I use a low flow rate for the return pump and a small sump because we also have a large, planted, remote display refugium. I don't need a large protein skimmer in the sump because it wouldn't be any better than the small one at removing waste.

Another problem with the "bigger is better" approach to protein skimmers is that you may not want everything organic suspended in the water removed, like phytoplankton. I have seen people buy phytoplankton from the store to feed filter feeders while emptying huge skimmers and pouring them down the drain.

One more important factor for determining skimmer size is knowing how dirty your water is in the first place. Skimmers are never the only source of filtration. How efficient are your other filtering strategies at removing suspended particles?

My point? Skimmer size section is way more complicated than how big your aquarium is.

 

[Reefable]

Good point


Sent from my iPhone using Tapatalk

 

[slief]

I have been in the hobby a long time, set up more than 10 reef tanks of various sizes. I also received some formal training and am currently working with the local school system to teach marine bio by maintaining a reef tank in the school. I have come to realize something that I have never seen discussed regarding sump protein skimmers. Specifically that size of tank does not determine size of protein skimmer needed. All protein skimmers say, "for up to a *** gallon tank." I have also seen people talk about going +1 on their skimmers to get extra clean water.

All of these approaches make several huge assumptions. First is that big tanks = big sumps with high flow rate. Sump size and flow rate are perhaps the most important indicators of optimal skimmer size. For example, if you have a 90 gallon tank and go to a 120 gallon tank, keep the same size sump and return pump flow, but add a larger skimmer, all you get is the same amount of suspended material in a bigger skimmer cup.

Here's another way of putting it. The skimmer in the sump only has access to the suspended organic waste material in the sump. It doesn't have access to the waste material in the display tank. Since it can only remove the waste it has access to, you need to increase the sump size and/ or return pump flow to get more production from your skimmer.

I have a 180 gallon reef tank in the school I work for. I use a low flow rate for the return pump and a small sump because we also have a large, planted, remote display refugium. I don't need a large protein skimmer in the sump because it wouldn't be any better than the small one at removing waste.

Another problem with the "bigger is better" approach to protein skimmers is that you may not want everything organic suspended in the water removed, like phytoplankton. I have seen people buy phytoplankton from the store to feed filter feeders while emptying huge skimmers and pouring them down the drain.

One more important factor for determining skimmer size is knowing how dirty your water is in the first place. Skimmers are never the only source of filtration. How efficient are your other filtering strategies at removing suspended particles?

My point? Skimmer size section is way more complicated than how big your aquarium is.

Let me try to provide some real facts to seperate from myths. "Proper" skimmer sizing is based on theoretical loads generated by fish waste and typical feeding. This is why most skimmer manufacturers provide a range of tank sizes for their skimmer. At the lower end of the range, a heavier load is assumed and at the higher end of the range, a lower load is assumed. In the case of Bubble King skimmers, a heavy load is considered roughly 1/2" of fish per display gallon. This number is widely recognized in the aquarium industry as a heavy load. This doesn't mean that all skimmer manufacturers follow that rule of thumb nor does it mean that all skimmer manufacturers rate their skimmer conservatively or optimistically.

The loads are generated in the display and not the sump. In fact, the sumps in our systems are ultimately used for reducing load and therefor should not be a factor when considering proper skimmer sizing. At least when it comes to properly rated skimmers. Again, many skimmer manufacturers rate this skimmers optimistically which is unfortunate as it leaves some guess work on the users part. The flow through the sump in my opinion is also pretty irrelevant when it comes to the skimmers ability to remove dissolved organics. High flow in the sump simply means that the skimmer will have the organics passed by it more frequently but once it catches up to the load, the flow in the sump will have little to no impact on the skimmer let alone the amount of dissolved organics a skimmer can continuously remove relative to the load that is being generated continuously.

As for going up +1.. That can often result in an inconsistent skimmer. A skimmer needs dissolved organics (proteins) to generate foam. In the absence of enough proteins, the skimmer will generate bubbles and not foam. It's the proteins that cause the bubbles to stick together which result in foam not bubbles. As the skimmer size gets larger, so does the neck diameter. As the neck diameter gets larger, so does the amount of dissolved organics required to generate enough foam to fill the neck. In the absence of enough DOC's, the skimmer will not be consistent because it will not be able to generate enough foam to keep the neck consistently full such that the foam overflows from the neck and results in skimmate. The end result is that the skimmer will be inconsistent and idle along until enough proteins build up in the water to allow the skimmer for fill the neck with foam. Unfortunately, the results in inconsistent water conditions because the dissolved organics will rise and fall on a regulars basis instead of remaing consistently low. Point being that a skimmer that is too large will not result in any more organics being removed from the water. There is no such thing as overskimming. It will however result in elevated levels of dissolved organics from time to time.

Lastly, things like filter socks have very little impact on skimmers. Skimmers removed dissolved organics. Solids on the other hand are often too heavy to attach to the bubbles in the skimmer and this is why skimmers will often collect detritus inside the body. As such, have one can only judge the cleanliness of the water based on the actual load because ultimately its the fish waste and dissolved food waste that the skimmer will be removing in addition to other dissolved organics and very small solids be it coral food or as you noted, plankton. That said, skimmers typically can only remove about 30% of the dissolved organics and as such, their impact on plankton is really pretty minimal in the grand scheme of things and shouldn't be something to worry about in a healthy reef well fed reef system.

 

[Luca_Brasi]

Proper skimmer sizing is based on theoretical loads. This is why most skimmer manufacturers provide a range of tank sizes for their skimmer. At the lower end of the range, a heavier load is assumed and at the higher end of the range, a lower load is assumed. In the case of Bubble King skimmers, a heavy load is considered roughly 1/2" of fish per display gallon. This number is widely recognized in the aquarium industry as a heavy load. This doesn't mean that all skimmer manufacturers follow that rule of thumb nor does it mean that all skimmer manufacturers rate their skimmer conservatively or optimistically.

I really don't see where you are disagreeing with me. Skimmer ratings are based on theoretical loads that make a lot of assumptions. But each system is different and bigger is not always better. Filter socks may not make a difference to skimmer production but flow rate and refugiums definitely do. So picking the best skimmer size is more involved than a theoretical load. It sounds like you are saying that skimmer ratings based on theoretical load are a good place to start. I'll agree with that.

 

[Tripod1404]

I guess this is one of the few advantages of a HOB skimmer that has direct access to water in main display.

 

[slief]

I really don't see where you are disagreeing with me. Skimmer ratings are based on theoretical loads that make a lot of assumptions. But each system is different and bigger is not always better. Filter socks may not make a difference to skimmer production but flow rate and refugiums definitely do. So picking the best skimmer size is more involved than a theoretical load. It sounds like you are saying that skimmer ratings based on theoretical load are a good place to start. I'll agree with that.

I went back and edited the first sentence of my post just prior to your reply. I wasn't really disagreeing and was more trying to point some stuff out thus the edit of my first sentence.. Since you are taking on the endeavor of educating others in a classroom environment and others who may not be as well informed, I figured I would lend my 2 cents.

As you probably know, I have been providing support for a well know skimmer manufacturer for a number of years here on this forum both in an unofficial and ultimately official capacity. I also help many others with skimmer issues as well. Back in the early 90's, I was involved in designing downdraft skimmers. I've messed with larger body skimmers converting them to mezzei injection as well. I've had more skimmers of different technologies (Mezzei, beckett, down draft, recirculating, wood stone etc) over the last 3 decades than most. Heck, here at my house, I have a couple Bubble Kings, an SCA, Euro Reef, AquaMaxx and even a 5' tall Klase skimmer that I imported around from Germany nearly 20 years. That Klase was way ahead of it's time and absotely state of the art back then and still would be today if Klase were still around. I only mention the above to lend some credibility to this discussion.

Flow rates through the skimmer can have a big impact on skimmer peformance because they impact the skimmers balance and stability. Too much flow and the skimmer will be unstable inside and tend to have a bubble line that surges up and down. The skimmer will also be inefficient and won't remove as much DOC's as it should. Too little flow and the skimmer won't generate good foam. Balance as you know is the key. Flow rates in the sump have little to no impact on skimmer performance unless the flow rate through the sump is much lower than the skimmers internal flow/skimmer pumps draw. Sadly most skimmer pump flow ratings are based solely on water flow and while they to often publish their SCFH numbers, the flow rates themselves don't usually account for the displacement of water flow that the air draw creates. In the case where the the skimmers flow rates are greater than the flow rates through the sump, the skimmer will tend to starve due to a lack of DOC's since it's circulating the water faster than it's coming through the sump. This can often result in increased DOC's in the display. Too fast of flow through the sump if there is such a thing will have little to no impact on the skimmer Performance.

As for refugiums having an impact, if they do, it's neglidgeable. Skimmers will have more of an impact on macro growth and the efficiency of the refugium. than macro growth will have on skimmer performance. Macro as you know feeds on nitrates and Po4. While the skimmer doesn't really remove Po4, nitrates are a biproduct of the DOC's that a skimmer removes. A refugium on the otherhand doesn't really remove DOC's. In short, they ultimately perform two different tasks. One being mechanical while the other is more biological. If anything, they overlap and both compliment our systems. There are many ATS advocates and refugium advocates alike that go skimmerless. While their nutrients are manageable and controlled, I personally like having both the fuge and skimmer and don't base my skimmer sizing on the presence of a refugium. As I said, the refugium will have little to no impact on the skimmer but the skimmer can impact macro growth. The water however will always be cleaner (more clear) with a skimmer.

 

[ca1ore]

I do agree that sizing skimmers based on tank size is not technically correct - they should be sized based on bio load and organics generated. Unfortunately there is no reliable way to determine specific bio load. Consequentially tank size is about the only proxy available to us. At least some skimmer makers qualify the sizing with light, medium and heavy stocking. Not terribly scientific, but it's what we have.

As to your other comments I mostly disagree. I have also been in the hobby for a very long time, have setup many tanks, and experimented with a lot of skimmers. I have neither noticed nor ever been presented with a cogent argument about skimmer performance being a function of either sump size or flow through the sump - beyond absurd minimums, that is. I suppose if a tank has inadequate internal circulation, a stronger return pump might move more detritus to the sump, but that's far more likely to just collect than be removed by the skimmer. In tanks where there is adequate internal circulation, a bigger pump just cost you more in electricity.

There may be a 'myth' that you have missed - that skimmers magically remove all organics in a single pass. They don't, and because they don't the size of and flow through this sump is practically irrelevant.

Flow through the actual skimmer is important, as is contact time. A skimmer, regardless of size, will only remove about 1/3 of the organics. That the addition of a bigger skimmer shows no increase in skimmate may simply be that the smaller one was big enough all along.

 

[victorcan]

My LFS store guys laughs at me every time I add a new component, I think I may just be addicted to chasing the ultimate sanitary tank lol, but heres my system in a nut shell. I run a 220 Display with over 20 fish 12 Large 4"-6"+ sized tangs a few 4"+ wrasses' and others that overflows into a 75 gallon fuge filled with 100-200 pulsing Xenia in one chamber and another 1/3 filled with Cheato overflowing to a 150 gallon sump (1/2 full) with 2 skimmers (a 500 gallon rated and a 250 gallon rated) with a bio pellet reactor, a UV sterilizer, and a 25 sq. ft micron filter. all being pushed by 2500 GPH return pumps (a iwaki rlt100 and a vector l1) my protein skimmer exhale nearly 5 gallons of nasty blackish brown sludge every 2-3 weeks.. Guy at Coralvue said I was overkill maybe I am? but my corals look insane and my fish have thrived with an immense amount of feeding fish food and 6 different kinds of coral food for nearly 2 years.. There is no one step meets all in this hobby and in all truth what one person says is crazy works well for another.. Guess what Im getting at is theres never enough or too much filtration if the wacko running the tank can utilize it LOL (and Im that wacko LOL) Happy reefing y'all

 

[tkeracer619]

I guess this is one of the few advantages of a HOB skimmer that has direct access to water in main display.

Unless it skims from the surface this is likely not the case. Since protiens head to thhe surface and overflow pushes them to the sump. A hob that pulls from under the surface may not have the concentration of docs that a sump would.

 

[Brunzy]

Thank you guys for this thread! As an up I commer to this hobby, this thread has helped me see both sides of the great debate.

 

[karimwassef]

What is too "big"?

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Build a 12foot DIY dual Beckett monster like this

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http://www.reefcentral.com/forums/showthread.php?t=2525951

 

[karimwassef]

I don't even use my skimmer to remove waste any more. I consider it the "lungs" of my tank and a key element in maintaining the chemical health of my tank.

 

[ksed]

I don't think that skimmer has enough contact time. Lol

 

[karimwassef]

That's why I made it recirculating. The through flow was ~2000 gph but the recirculating loop was ~4000 gph. So the water inside turned three times through the 96" middle section and went through the high volume air injectors at least twice before escaping.

The flow through the sump loop is 6000gph so most of the tank water makes its way through the sump frequently from the end to end 96" weir.

I'd say most of the tank water found its way into the skimmer and then spent quite some time in it.

 

[Luca_Brasi]

What is too "big"?

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http://www.reefcentral.com/forums/showthread.php?t=2525951

Can't argue with results. Looks good

 

[Luca_Brasi]

That's why I made it recirculating. The through flow was ~2000 gph but the recirculating loop was ~4000 gph. So the water inside turned three times through the 96" middle section and went through the high volume air injectors at least twice before escaping.

The flow through the sump loop is 6000gph so most of the tank water makes its way through the sump frequently from the end to end 96" weir.

I'd say most of the tank water found its way into the skimmer and then spent quite some time in it.

Can't argue with results.

 

[karimwassef]

That's why I made it recirculating. The through flow was ~2000 gph but the recirculating loop was ~4000 gph. So the water inside turned three times through the 96" middle section and went through the high volume air injectors at least twice before escaping.

The flow through the sump loop is 6000gph so most of the tank water makes its way through the sump frequently from the end to end 96" weir.

I'd say most of the tank water found its way into the skimmer and then spent quite some time in it.

But I still primarily use it to equilibrate to the atmosphere.

 

[Tripod1404]

Thank you guys for this thread! As an up I commer to this hobby, this thread has helped me see both sides of the great debate.

U use a reef octopus classic 90 HOB in one of my smaller tanks. It skims from the surface.

 

[karimwassef]

I don't even use my skimmer to remove waste any more. I consider it the "lungs" of my tank and a key element in maintaining the chemical health of my tank.

I think the thread broke. Sorry

 

[Lsufan]

I do agree that sizing skimmers based on tank size is not technically correct - they should be sized based on bio load and organics generated. Unfortunately there is no reliable way to determine specific bio load. Consequentially tank size is about the only proxy available to us. At least some skimmer makers qualify the sizing with light, medium and heavy stocking. Not terribly scientific, but it's what we have.

As to your other comments I mostly disagree. I have also been in the hobby for a very long time, have setup many tanks, and experimented with a lot of skimmers. I have neither noticed nor ever been presented with a cogent argument about skimmer performance being a function of either sump size or flow through the sump - beyond absurd minimums, that is. I suppose if a tank has inadequate internal circulation, a stronger return pump might move more detritus to the sump, but that's far more likely to just collect than be removed by the skimmer. In tanks where there is adequate internal circulation, a bigger pump just cost you more in electricity.

There may be a 'myth' that you have missed - that skimmers magically remove all organics in a single pass. They don't, and because they don't the size of and flow through this sump is practically irrelevant.

Flow through the actual skimmer is important, as is contact time. A skimmer, regardless of size, will only remove about 1/3 of the organics. That the addition of a bigger skimmer shows no increase in skimmate may simply be that the smaller one was big enough all along.

This is how I have always felt about skimmers